MCQOPTIONS
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MCQOPTIONS
This section includes 18 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Machines knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
A_POLYPHASE_INDUCTION_MOTOR_OF_THE_SLIP_RING_OR_WOUND_ROTOR_TYPE_CAN_BE_USED_____________?$ |
| A. | for high start-up torque applications |
| B. | as a frequency converter |
| C. | any of the mentioned |
| D. | none of the mentioned |
| Answer» D. none of the mentioned | |
| 2. |
IN_AN_AC_MACHINE,_THE_EFFECT_OF_DISTRIBUTING_THE_TURNS_IN_DIFFERENT_SLOTS,_RESULTS_IN_A_FURTHER_REDUCTION_OF_GENERATED_EMF_BY_THE_FACTOR_KD._THIS_FACTOR_IS_CALLED_____________?$ |
| A. | distribution/speed factor |
| B. | coil pitch factor |
| C. | winding factor |
| D. | any of the mentioned |
| Answer» B. coil pitch factor | |
| 3. |
If the rotor of an induction motor is made to revolve in a direction opposite to the rotating flux wave, then RMS value of EMF induced in one phase of rotor E is proportional to ____________$ |
| A. | 2-s |
| B. | s |
| C. | 1-s |
| D. | 2+s |
| Answer» B. s | |
| 4. |
The equation for slip speed is ____________$ |
| A. | (ω-ω<sub>r</sub>)/ω |
| B. | ω-ω<sub>r</sub> |
| C. | (ω<sub>r</sub>-ω)/ω |
| D. | ω<sub>r</sub> |
| Answer» C. (‚âà√¨‚àö¬¢<sub>r</sub>-‚âà√¨‚àö¬¢)/‚âà√¨‚àö¬¢ | |
| 5. |
The DC machines are designed with flat topped flux density waves because |
| A. | average value of brush voltage is more for a flat topped B-wave |
| B. | average value of brush voltage is less for a flat topped B-wave |
| C. | losses for flat topped B-wave are less |
| D. | none of the mentioned |
| Answer» B. average value of brush voltage is less for a flat topped B-wave | |
| 6. |
The short pitch winding for an alternator gives |
| A. | improved wave form of the generated EMF per phase |
| B. | reduced value of self inductance of the winding |
| C. | increased rating of machine |
| D. | reduced tooth ripples |
| Answer» C. increased rating of machine | |
| 7. |
A 6 pole machine is rotating at a speed of 1200rpm. This speed in mechanical rad/sec and electrical radians per second is respectively |
| A. | 40π, 40π/3 |
| B. | 120π, 40π |
| C. | 20π, 60π |
| D. | 40π, 120π |
| Answer» E. | |
| 8. |
If the dimensions of all the parts of a synchronous generator and the number of field and armature turns are doubled, then the generated voltage will change by a factor of |
| A. | 1 |
| B. | 2 |
| C. | 4 |
| D. | 8 |
| Answer» E. | |
| 9. |
The EMF generated in an alternator depends upon |
| A. | speed |
| B. | maximum flux per pole |
| C. | series turns per phase |
| D. | phase spread |
| Answer» C. series turns per phase | |
| 10. |
In an alternator, frequency per revolution is equal to |
| A. | number of poles |
| B. | twice the number of poles |
| C. | speed in rps |
| D. | number of pole-pairs |
| Answer» E. | |
| 11. |
A winding is distributed in the slots along the air gap peripher? |
| A. | to add mechanical strength to the winding |
| B. | to reduce the amount of conductor material required |
| C. | to reduce the harmonics in generated EMF |
| D. | to reduce the size of the machine |
| Answer» E. | |
| 12. |
The effect of short pitched coil on the generated EMF is _____________ |
| A. | increasing |
| B. | decreasing |
| C. | either increasing or decreasing |
| D. | none of the mentioned |
| Answer» C. either increasing or decreasing | |
| 13. |
Which of the following equations represents the RMS value of the generated EMF in a short-pitched N-turn armature coil of an AC machine ____________ |
| A. | E = √2πk<sub>p</sub>f<sub>r</sub>NΦ |
| B. | E = 2πk<sub>p</sub>f<sub>r</sub>NΦ |
| C. | E = NΦω<sub>r</sub>k<sub>p</sub>sinω<sub>r</sub>t |
| D. | None of the mentioned |
| Answer» B. E = 2‚âà√¨‚àö√ëk<sub>p</sub>f<sub>r</sub>N‚âà√≠¬¨‚àÇ | |
| 14. |
In a short pitched coil, the coil pitch factor kp, is given by ____________ |
| A. | k<sub>p</sub> = cosε |
| B. | k<sub>p</sub> = cosε/2 |
| C. | k<sub>p</sub> = √2πf<sub>r</sub>NΦcosε |
| D. | k<sub>p</sub> = cosε/2cosω<sub>r</sub>t |
| Answer» C. k<sub>p</sub> = ‚Äö√Ñ√∂‚àö‚Ć‚àö‚àÇ2‚âà√¨‚àö√ëf<sub>r</sub>N‚âà√≠¬¨‚àÇcos‚âà√≠¬¨¬µ | |
| 15. |
In AC rotating machines, the generated or speed EMF |
| A. | leads Φ by 90° |
| B. | lags Φ by 90° |
| C. | is in phase with working flux |
| D. | lags Φ by 180° |
| Answer» C. is in phase with working flux | |
| 16. |
In the equation for RMS value of the generated EMF in a full pitched coil of an AC machine, |
| A. | |
| B. | rotating speed of the armature coil |
| C. | rotating speed of the flux density wave |
| Answer» D. | |
| 17. |
The EMF equation e = NωrΦsinωrt is applicable to ____________$ |
| A. | AC systems with time variant field flux |
| B. | DC systems with time variant field flux |
| C. | Both AC and DC systems with time invariant field flux |
| D. | Both AC and DC systems with time variant field flux |
| Answer» D. Both AC and DC systems with time variant field flux | |
| 18. |
Which of the following statements is/are correct regarding the generation of EMF in rotating electrical machines in the armature winding? EMF is generated ____________ |
| A. | by rotating armature windings through a magnetic field |
| B. | by rotating magnetic field with respect to the armature windings |
| C. | by designing the magnetic circuit to have variable reluctance with rotor rotation |
| D. | any of the mentioned |
| Answer» E. | |